Accumulating evidence suggests that emergence of a stem-like state in the tumor and adaptation to host immune defenses are responsible in large part for disease progression and recurrence in cancer patients. Thus, it is important to understand the mechanisms through which the tumor acquires a stem-like condition and evades immune surveillance to reduce the mortality rate due to cancer. We recently demonstrated that through immune selection, cancer cells experience upregulation of Nanog, a master transcription factor, which is fundamental to the maintenance and self-renewal of pluripotent stem cells. Upregulation of Nanog results in a stem-like and immune-resistant phenotype of these cancer cells. Accordingly, inhibition of Nanog renders tumor cells susceptible to killing by CD8+ cytotoxic T lymphocytes (CTLs) in mice. Furthermore, we found that Nanog is abundant in many different human cancer types, and upregulation of Nanog in tumor tissue correlates with the disease stage and overall survival of patients with cervical neoplasia. Thus far, our studies have identified Nanog as an ideal molecular target for cancer therapy and suggest a link between the stem-like state in cancer and immune surveillance. The primary purpose of the current project is to investigate the role of Nanog in tumor immune escape through modification of the tumor microenvironment. We hypothesize that, in the natural course of host immune surveillance, cancer cells progress towards upregulation of Nanog and that Nanog creates a microenvironment that protects the tumor cells from killing by CTLs. Specifically, we propose to: (1) Characterize real-time tumor evolution towards upregulation of Nanog expression in live animals during a tumor-specific immune response; (2) Characterize the role of Nanog in the establishment of an immune- suppressive tumor microenvironment; and (3) Characterize the molecular mechanisms by which Nanog mediates immune escape. The successful completion of this project will provide substantial insight into the mechanisms that mediate tumor adaptation in the natural setting of the host immune system. Furthermore, it will establish a platform technology to investigate tumor evolution in real-time at the molecular level. Additionally, this project introduces and evaluates the concept that the stem-like phenotype of cancer may arise through immune surveillance and mediate immune escape. The results of this study will have significant clinical implications for the therapeutic intervention of cancer.